Preparation

Mix the sifted flour in a bowl with the cocoa, cinnamon and pinch of salt

Cut the butter into small pieces and blend to a creamy consistency in a food processor

Add the superfine sugar and vanilla extract to the creamy butter

Process again until the mixture becomes a nice, even dough. Add the sifted flour/cocoa/cinnamon/salt mixture. Blend well

Form the dough into 2 balls

Place both balls of dough in the refrigerator for 30 minutes

Next, make each ball of dough into a sausage shape of about 1½″ (4 cm) in diameter, taking care to press the dough down well with the palm of your hand before rolling it to avoid air pockets

Roll each sausage up in clear plastic wrap and place in the refrigerator for 2 hours

Preheat the oven to 350°F (180°C)

Beat the egg yolk in a small bowl until it is completely liquid

Remove the rolls of cookie dough from the refrigerator and cut them into discs about ½″ (1½ cm) thick

Use a pastry brush to coat each disc with a little egg yolk

Cover a baking sheet with parchment paper and sprinkle it with crystallized sugar

Roll each side of the cookie dough discs in the crystallized sugar, pressing gently so that the sugar sticks

When all of the discs are arranged on the baking sheet, give them another sprinkling of crystallized sugar

Cover another 2 baking sheets with parchment paper

Put the rest of the cookies on them, leaving about 1″ (2½ cm) between each cookie

Bake for 15 to 18 minutes, changing the baking sheets around in the oven about halfway through cooking and turning them 180°

To make sure that the cookies are properly cooked, check they are firm to the touch before removing them from the oven

Remove the cookies from the oven and let them cool down on a cooling rack.

Suggestion

These “diamonds” are known as mignardises - small, sweet nibbles that you can serve with a cup of coffee or tea, along with a few pralines or wafers. Their soft/crunchy combination is irresistible
Feel free to serve these “diamonds” with a fresh fruit salad or even with a vanilla custard or ice cream.